1. Field of the Invention
The invention generally relates to a geometric error measuring device. More particularly, the invention relates to a geometric error measuring device which uses non-contact, optical measurement to measure geometric errors and which is highly accurate.
2. Description of the Prior Art
Laser interferometer has often been used in the measurement of geometric errors of machines and has been regarded as a very accurate measuring device. Because laser interferometer is characterized with large measurement range and nano level resolution, it has been used to measure geometric errors of many types of high-precision machines, such as CNC machines, CMM's (coordinate measuring machines), high-precision grinding machines and semiconductor manufacturing machines.
However, laser interferometer has not been widely used in the regular plants because of its high price. A laser interferometer with only the basic module of position error measurement has a price tag of NT$ 0.6 million; therefore regular plants can not afford it. A laser interferometer with the complete set of modules (including the modules for the measurement of straightness, squareness and rotational angles) costs more than NT$ 1.5 million. In addition, each module can measure only a certain type of error and each module requires different type of setup or arrangement; therefore, these factors further affect the willingness of using it.
Because each type of setup and the adjustment of the setup take time, methods and measuring systems have been developed to perform the measurement of several types of geometric errors simultaneously. In addition, a larger reflective lens has been used; however, in the set-up, such lens has to be perpendicular with the incident laser ray and other obstacles are yet to be overcome.
Therefore, to substantially lower the cost, we have developed a simple geometric error measuring device, which utilizes collimated light and at least one (quadrant) photodiode to measure errors in straightness, squareness and rotational angles (pitch, yaw and roll).
Moreover, in the geometric error measuring device of the present invention, three types of configurations or arrangements (for the measurement of straightness, squareness and rotational angles) have been used to simplify the measuring process and make it easier to use.